The invention relates to a flow controlling apparatus for use with a power steering device in which a hydraulic fluid discharged from a pump is delivered to a power steering device through a throttled passage and an excess flow is returned to the suction side of the pump through a bypass passage, and more particularly, to such flow controlling apparatus which reduces the flow delivered to the power steering device as the number of revolutions of the pump increases.
A pump unit which is used in a power steering device of an automobile is provided with a flow regulating valve, which operates to maintain a constant flow to the power steering device by increasing the flow area of the bypass passage as the running speed of the automobile and hence the number of revolutions of the pump increases, thereby bypassing the majority of the flow discharged from the pump to the suction side thereof. When the automobile is running at a high speed, it is required that the steering reaction sensed by a driver be increased as the running speed increases, and at this end, the control flow to the power steering device is reduced in response to an increase in the number of revolutions of the pump. This also contributes to a power saving when the vehicle is running at a high speed.
However, many of conventional flow controlling apparatus of this kind is arranged to control the throttled passage having a variable area in accordance with a displacement of the flow regulating valve. This allows a predetermined flow decrease characteristic to be achieved during the time the power steering device is not loaded, but when the pressure is applied in order to operate the power steering device, the flow regulating valve functions to restrict the bypass flow, thus unfavourably causing a restoration of the flow which has once been decreased.